What's in a Medicine F334

Carboxylic Acids

As carboxylic acids are weak acids, they are able to partially dissociate in water to form an oxonium ion (H3O+) and a carboxylate ion (COO-):

HCOOH(aq) + H2O(l) <---- ----> H3O+(aq) + HCOO-(aq)

They're also able to react with bases to form salts (acid + base = salt + water):

CH3COOH(aq) + NaOH ----> CH3COO-Na+(aq) + H2O(l)

Although they're weak acids, carboxylic acids are able to react with carbonates to produce carbon dioxide. Sodium carbonate or sodium hydrogencarbonate are most commonly used:

2HCOOH(aq) + Na2CO3(aq) ----> 2HCOO-Na+(aq) + CO2(g) + H2O(l)

This reaction produces bubbles fo carbon dioxide gas which can be tested with limewater, which will turn milky in the presence of CO2.

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Acidic Properties

Alcohols, phenols and carboxylic acids are all weak acids and can react with water to produce oxonium ions. Their order of acid strength is:

Alcohol < water < phenol < carboxylic acid

Carboxylic acids are stronger than phenols because they're able to react with carbonates to form carbon dioxide, water and a salt whereas phenols don't react with carbonates. The relative strength of each compound can also be explained by the stability of their anion. Phenoxide ions and carboxylate ions are much more stable than hydroxide and ethoxide ions because the negative charge on the ion can be delocalised across several atoms in the compound.

Alcohols react with neither bases nor carbonates

Phenols react with bases but not carbonates

Carboxylic acids react with both bases and carbonates

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Mass Spectrometry

Mass spectrometry can be used to determine the structure of molecules. This can be done by identifying the molecular ion peak which is the peak with the largest m/z ratio, or furthest to the right on the x-axis. It can also be used to determine the fragments produced when the molecular ion is unstable and breaks up in a process called fragmentation.

Every line in the spectrum corresponds to a positively charged ion and the molecular ion peak. Other lines represent fragments of the molecular ion or isotope peaks. The base peak is the peak with 100% intensity.